I want to know what optics they are using. On segments that are 7,000 miles long - are there active optic splice boxes along the length of the cable? Or are they using lasers that actually push 7K miles?
Submarine cable systems often employ repeaters (hardened EDFAs). I remember one vendor bragging that not one of their units had EVER failed in service.
That PDF is great, thanks. Jesus - they are huge. Earlier in the PDF, they appear small.
Is that a single strand they are amplifying with these? I'd like to find cost figures for how much it is to run a single fiber trans-oceanically (if thats a word).
They talk about it in the PDF. Apparently they use a 1400nm laser along the same fiber that excites some receptor, which provides the power for the amplification.
The diagram of the Polar King cable-laying ship that gk1 posted here shows a "repeater stack" near the holds full of cable. I assume the repeaters are spliced into the cable as it's being laid. http://en.wikipedia.org/wiki/Submarine_communications_cable#... describes the repeaters in a modern submarine telephone cable, and says: "The optic fiber used in undersea cables is chosen for its exceptional clarity, permitting runs of more than 100 kilometers between repeaters to minimize the number of amplifiers and the distortion they cause."
They are "powered" by lasers themselves. No electronics involved; excess energy from a pumping laser boosts the intensity of the data laser, using sections of special doped fiber.
That's very cool, but the "submarine communications cable" article I linked to above claims that the repeaters are powered by DC fed through a single conductor in the middle of the cable, though it doesn't cite a source for that information.
I wouldn't be surprised if both methods have been used in different situations or at different times.
Are you saying that there's an extra "pumping fiber" in the bundle, fed by a pumping laser on shore? Or are the pumping lasers in the repeaters, in which case there would still need to be electrical power supplied down the cable to drive the pumping lasers?
The DC may be likely for old-style repeaters, as Er-doped fiber amplifiers are (relatively) new.
It's my understanding that the pumping laser would be a different wavelength carried by the same fiber (just as a fiber can carry multiple data channels using different wavelengths in DWDM). The boost happens because of the special doped section.
The pumping laser essentially puts the doped medium in an energy condition where the data transmission can stimulate additional emission (similar to how lasers work in the first place). Few photons in, many out. The energy required to do so comes from the pumping laser.
But seriously, that is damn cool - while I have been in IT/networking for a long time - I was not aware of "pumping lasers" as everything I have done, even in designing massive fiber cable plants have all been for relatively short distances.
